Regeneration medicine is the area of advanced medicine that aims at repairing tissues and organs of diseased portions of the body by means of results from studies of mechanisms behind the development and organization of tissues and organs of living organisms. It is ideal that treatment be enabled by the repair capability of the patient's tissue. Hence, a likely approach to regeneration medicine is to develop a method of maximizing the potential repair capability of tissues of living organisms. To this end, it is necessary to elucidate and utilize the functions of regulators that regulate cell growth, cell differentiation, and tissue organization, such as cytokines and matrix molecules. Meanwhile, it is necessary to proliferate cells for use in transplantation therapy by in vitro culture. Hence, stem cells, which are capable of producing a wide variety of functional cells while self-proliferating for a long time, like tissue stem cells, are drawing attention.
As an example of regeneration medicine, cell medicine can be mentioned. Cell medicine refers to the art of treating disease using the patient's own tissue or another person's tissue. Cell medicine is considered to enable the proliferation of immunocytes to increase the immunizing power thereof, the cultivation of chondrocytes and transplantation thereof to joints, and the like. Among the target cells for which cell medicine is expected to be effective are hematopoietic stem cells for treating bone marrow suppression after cancer chemotherapy. Hematopoietic stem cells are used to prevent bone marrow suppression after treatment for myelocytic leukemia and cancer chemotherapy by a method comprising collecting hematopoietic stem cells from peripheral blood and the like in advance, treating them with a cell growth factor, antigen and the like, and then transplanting them.
As a representative example of cell medicine, umbilical cord blood stem cell transplantation is described below. Umbilical cord blood stem cell transplantation refers to collecting blood from the umbilical cord between the newborn and mother (umbilical cord blood), preserving it under freezing, and transplanting it to a leukemia patient and the like if necessary. Umbilical cord blood is rich in hematopoietic stem cells. Hence, hematopoietic potential is obtained even with much smaller amounts of cells than bone marrow and peripheral blood. Additionally, transplantation is possible even if there is no complete matching of HLA type, and the incidence of graft-versus-host disease (GVHD) is low. However, because the number of cells collected is limited, the currently prevalent practice is transplantation to children.
One of the essential infrastructures in regeneration medicine is the art of culturing target cells. This art is required to be of a level that ensures the proliferation (including differentiation and expansion) of target cells stably, in large amounts, at low costs, quickly, and conveniently. There are roughly two methods of cell culture: serum culture, which comprises culturing target cells using a serum-containing medium, and serum-free culture, which comprises culturing target cells using a serum-free medium, with the latter drawing attention for the reasons of the prevention of contamination with viruses and prion and the like in regeneration medicine settings. In particular, to clinically apply ex vivo expansion of umbilical cord blood, which is commonly used as a source of the cells, and the art of expansion culture of umbilical cord blood progenitor cells, it is an important task to establish a method of serum-free culture.
Regarding the expansion culture of hematopoietic cells in a serum-free medium, some related arts are known.
For example, WO98/06822 discloses a serum-free medium containing recombinant human serum albumin, but gives no description on the expansion culture of hematopoietic cells.
WO95/06112 discloses preparing hematopoietic stem cells from umbilical cord blood, and culturing them in a serum-free medium containing human serum albumin. There is also a description that cells that have been cultured under serum-free conditions tend to be undifferentiated. However, WO95/06112 essentially relates to the proliferation of neutrophil progenitor cells and megakaryocyte progenitor cells.
Furthermore, WO97/33978 discloses culturing CD34+ cells prepared from umbilical cord blood in a serum-free medium containing human serum albumin, and achieving the expansion of CD34+ cells by the cultivation. However, the use of recombinant human serum albumin in the cultivation is not disclosed.